CwftS'LAAS— 953 (o 6 CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE LABORATOIRE DANALYSE ET ©’ARCHITECTURE DBS SYSTEMES S.L ENGINE IDLE CONTROL IMPROVEMENT BY USING AUTOMOBILE REVERSIBLE "ALTERNATOR” L. KOUADIO, P. BID AN, M. VALENTIN, J.P. BERRY LAAS REPORT 95268 JUNE 1995 DISTRIBUTION OF THIS DOCUMENT IS INJURED FOREIGN SALS PROHIBITS) ftn 6& LIMITED DISTRIBUTION NOTICE This report has been submitted for publication outside of CNRS It has been issued as a Research Report for early peer distribution DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document S.I. ENGINE IDLE CONTROL IMPROVEMENT BY USING AUTOMOBILE REVERSIBLE “ALTERNATOR” L.K. Kouadio, P. Bidan, M. Valentin, J.P. Berry L.A.A.S./C.N.R.S., 7 Avenue du Colonel ROCHE, 31077 Toulouse Cedex FRAACF. Phone: (33) 61.33-64-17; Fax: (33) 61.55.35.77; e-mail: [email protected] Abstract. This paper describes an original method for engine idle improve­ ment. It is well known that inappropriate idle-speed control increases fuel consumption, pollutant emissions and also reduces the idle quality. To prevent engine stalling and improve its performance during idling it is proposed a strategy based on two control loops such as that of the tra­ ditional air-flow ratio and an other providing an external supplementary torque via the automobile’s reversible “alternator”. Hence engine stalling is prevented due to the faster torque response and secondly Fuel/Air ratio is easily controllable due to the slow variation of the intake air-flow. Keywords. Spark-Ignition Engine, Idle-speed control, Electrical assistance, Synchronous machine, Fuel Control, Automotive emissions, Multi-input system 1. INTRODUCTION others) to reduce pollutant emissions and fuel consump­ tion. Furthermore car driveability improvement depends Spark ignition engine is nowadays the mostly used en­ on the smallness of torque fluctuation during idling. Un­ gine in automotive design because of its better power to fortunately, a lower speed causes engine stability deteri­ weight ratio despite its relatively low efficiency around oration and increases the engine sensitivity to external 30% combined with the high lower heating value of the torque disturbance (Nishimura and Ishii, 1986). To solve fuel. Nevertheless, all the politics of energy savings and the above mentioned problems this paper proposes to environment protection initiated since the last twenty include an external torque control loop within the auto­ years call for many interrogations. Thus we have to think mobile reversible “alternator”. The reasons behind this about the necessary improvements in the engine opera­ approach is to avoid large throttle opening gradient and tion. While “cruising speed” phases are considered to be thereby to reduce the air intake nonlinearities effects on more or less clean, the transient are difficult to control. the control. In this way, an accurate F/A ratio is easily In particular the optimal Fuel/Air (F/A) ratio control attainable to allow the three-way catalyst converters to is more difficult to realize in transient due to the in­ keep to the bearable ±0.3% excursions from the stoichio­ take subsystems nonlinearities and dynamics (Aquino, metric conditions (Amstutz, 1994). The main novelty of 1981; Bidan et al. 1993; Bidan et at., 1995). As a con­ the system resides in the fact that the electrical machine sequence. fuel consumption and pollutant emissions in­ based the torque generation is the automobile “alterna­ creases (Braun el al., 1988). Concerning the idling it tor” . This machine is a Wound-Rotor Synchronous Ma­ is known that lower idle-speed is one method (amongst chine (S.M.) and is controlled to be able to operate in drive motor phase while improving its traditional use 3. S I. ENGINE MODELING as an alternator. Fig.l shows the overall system block diagram. Various models of S.I. engine have been presented in the past twenty years (Dobner, 1980). To achieve a control- oriented model the system was considered through the mean values of the state variables and divided in three Tracking basic subsystems as shown in Fig.2. Controller Spark advance Throttle opening Air flowrate Torque r.h Mechanical Speed Generation N r Injection time Fuel/Air ratio Engine T orque Dynamics Combustion) Engine Synchronous Regenerative Battery Machine AC-DC Fig. 2. S.I. engine model description Converter The study of this model clearly shows two fundamental Fig. 1. Functional block diagram of the Idle-speed con­ dynamics in the intake manifold. The first one concerns trol system the air filling effect due to the intake manifold volume and the second one depends on the wall wetting by the fuel. In this paper it is considered that the electronic injection device compensate the fuel film dynamic to 2. ENGINE IDLING PROBLEMS maintain the Fuel/Air ratio (r*) to its nominal point during transients. Spark advance (a) is also supposed Engine idling has always revealed itself in terms of en­ to its nominal value. Thus, the throttle opening (<£) is ergy savings, reduction of pollutant emissions and also the only engine parameter available for the idle-speed in terms of idling quality which supposes a constant av­ control considered here. erage idle-speed and a minimum oscillation. However, when oscillations increase with weaker idle-speed, stabil­ ity degradation may occur following such uses as air con­ ditioning and power steering etc, which in worst cases, 3.1 Air intake subsystem model will cause the engine to stall. Hence the crucial question about how to reduce engine idle-speed and at same time The air intake subsystem is governed by nonlinear equa­ improve its robustness with respect to disturbances. Sev­ tion where the manifold pressure (Pm) is the state vari­ eral works have been concerned with automotive en­ able. Taking Tm to be the manifold temperature, Pa at­ gine idle-speed control. HITOSHI (Inouie and Washino, mospheric pressure, R the gas constant of the mixture, 1990) proposes an idle-speed control system based on Mq the air molar mass, 7 the air specific heat ratio, compensating the variation of the alternator’s current Mjvc the air mass that can be absorbed by each cylin­ seen as a load disturbance. This control induces throttle der in normal conditions, ma the air mass really entering opening and thereby anticipates idle-speed drop. Also into a cylinder per stroke, Vbdc the cylinder volume at air-how ratio and spark-advance are more thoroughly bottom dead center and n the number of cylinder respec­ studied by other authors (Aquino, 1981; William and tively, we consider the following nonlinear equations de­ Citron. 1984; Francis and Fruechte, 1983) to perform en­ scribing the air intake subsystem (Dobner, 1983; Moska gine idle-speed control. The solution proposed here has and J.K.Hedricks, 1992; Chaumerliac et al, 1994): t he dist inctive feature of combining the traditional air­ flow ratio control (via an electric throttle actuator) si­ multaneously with the S.M. operating as a synchronous Or(*)FWr,,) motor, to provide a supplementary torque. This control 120 approach leads to a multivariable system with, on the -[Pm-fr(A)] one hand two input variables defined by the throttle opening and the synchronous machine R.M.S. current (1) and on the other hand one output represented by the engine speed. The purpose of this configuration is to whe take advantage of the S.M. faster torque response to / 27 9(rp) = - r„ impose a smooth gradient of the throttle opening. 7 - 11 l2QRTm f' __ A/pV rr, 3.3 Linear idle modeling of the engine rcrit ' -y+1 ■ Before establishing the overall idle model of the engine, Pm >f ^ Fcrit the relation governing the rotational dynamics is here Pa modeled with a constant inertia J and given by the well r crit 7 ^ l*crit known mechanics law: ^(30^^^ " AF;& - AFfood (5) and Cr($) is the aeraulic resistance of the throttle, ra is the engine air intake ratio (normalized value). Pr is a Hence, all the equations established so far lead us to the partial pressure depending on acoustic phenomenon. linear engine idling model below (see Fig.3), deriving In this paper given that our purpose consist of control­ from Dobner’s idling linear small signal model (Francis ling the idle-speed of a four-cylinder engine at the vicin­ and Fruechte, 1983). ity of a nominal speed the linearisation of system (1), for small perturbations, yields ( —A Pm = — (A"$A<F — A.vpAPm — KpxAN) ^ 1 Ara = KrpAPm + KrNAN (A) denotes a small fluctuation around a nominal point. 3.2 Engine Torque modeling Fig. 3. Linear small signal model of the engine idling Modeling the average of the engine torque consist in a re­ lationship between the engine control parameters (such as the spark advance a, the mixture F/A ratio r,, the air-mass ratio ra into the cylinder and the engine speed 4. ELECTRICAL ISSUES .V) to yield the torque at any speed. For this, assum­ ing an optimal spark advance the following relation has As explained previously, the principle of the proposed been experimentally identified: Idle-speed Control System (I.C.S.) is based on the ca­ pability of the automobile’s Synchronous Machine to F,/! = a0[l - ki(ri{t - To) - rim)2]ra{t - To) operate in motor phase and thus sustain the S I. en­ —o,i — an A (t) — a3N 2(t) (3) gine in idling phase. In this way to perform the control system some experiments and tests have been made on where rim is the Fuel/Air ratio which yields the maxi­ 1.5KW automobile “alternator”. The main test consists mum torque, F^ is the engine torque.